Cyclotrons are widely applied in the field of nuclear medicine, especially in the fields of radiopharmaceuticals, tumor treatment, etc. A host system of a superconducting cyclotron accelerates ions by using an electromagnetic field of a resonant cavity, and a tuning ring is an important part to realize the tuning of the resonant cavity. The tuning ring should be able to make slight adjustment of a RF cavity frequency in real time, whether under a stop condition or an operation condition of the cyclotron. Therefore, it is necessary that the electrical contact between an electrical contact member and an inner and an outer sleeve wall is performing well and that the electrical contact member can slide up and down freely, which puts forward very high requirements for the electrical contact, thermal coupling, pressure resistance and service life, etc. of the contact. However, the traditional electrical contacts are prone to wear wall surfaces. Moreover, in the tuning ring adjustment process, there is a relatively large line current density, which may generate an instantaneous current, easily causing sparking phenomenon and electromagnetic interference to the RF cavity. In order to solve the above problems, a solution is now provided.